Enhancing reversible hydrogen storage performance of 2LiBH ₄ –MgH ₂ via in‐situ building heterogeneous nucleation sites

Abstract

Abstract 2LiBH 4 –MgH 2 composite is one of the most attractive reactive hydride composites with a theoretic hydrogen capacity of 10.8 wt%. However, the large nucleation restriction of MgB 2 during the second step of dehydrogenation results in sluggish hydrogen storage kinetics and high operating temperature, which hinders its practical application as on‐board hydrogen storage materials. Herein, Al 3 Ti doped Al nanoparticles (AT NPs) are prepared by a facile chemical reduction reaction to improve the hydrogen storage performance of 2LiBH 4 –MgH 2 composite. During the initial H 2 desorption process, MgAlB 4 and TiB 2 that have identical crystal structure and low d ‐value mismatch with MgB 2 resulting from the reaction between AT NPs and 2LiBH 4 –MgH 2 composite serve as effective nucleation sites for the formation of MgB 2 . As a result, the apparent activation energy of the two‐step H 2 desorption of AT NPs doped 2LiBH 4 –MgH 2 composite are notably decreased to (110.0 ± 5.9) and (119.6 ± 1.4) kJ·mol −1 , which is 55.5 and 33.5 kJ·mol −1 lower than that of the undoped sample. More importantly, a reversible hydrogen storage capacity of 9.2 wt% after 10 cycles of H 2 desorption and adsorption could be achieved, corresponding to a capacity retention rate of 99%. The building of reactive bimetallic catalyst towards in situ formation of heterogeneous nucleation sites provides a new strategy for improving the hydrogen storage performance of reactive hydride composites.